Rearrange pg_subtrans handling as per recent discussion. pg_subtrans

updates are no longer WAL-logged nor even fsync'd; we do not need to,
since after a crash no old pg_subtrans data is needed again.  We truncate
pg_subtrans to RecentGlobalXmin at each checkpoint.  slru.c's API is
refactored a little bit to separate out the necessary decisions.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b9d0398b621..5c07795c8a9 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.162 2004/08/12 19:03:23 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.163 2004/08/23 23:22:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4918,6 +4918,14 @@ CreateCheckPoint(bool shutdown, bool force)
 	if (!shutdown)
 		PreallocXlogFiles(recptr);
 
+	/*
+	 * Truncate pg_subtrans if possible.  We can throw away all data before
+	 * the oldest XMIN of any running transaction.  No future transaction will
+	 * attempt to reference any pg_subtrans entry older than that (see Asserts
+	 * in subtrans.c).
+	 */
+	TruncateSUBTRANS(GetOldestXmin(true));
+
 	LWLockRelease(CheckpointLock);
 }